High speed, high performance machines need stable, low friction bearings in order to operate smoothly and efficiently. The electronics industry has provided numerous new developments for high speed bearings, used, for example, in hard disc drives, laser printers and other electronic equipment where speeds in excess of 10,000 rpm are needed. These bearings typically use a gas, specifically air, as a lubricant.
Such bearings as described in the prior art have not been shown to perform in applications where high temperatures in addition to high speed may be encountered. In particular, gas turbine engine manufacturers are seeking engine main shaft bearings capable of operating up to temperatures of 700° F. and 4 million DN, where DN is the speed parameter, the product of bearing bore diameter in mm and shaft rotative speed in rpm (revolutions per minute). Such operating conditions are beyond the capability of conventional ball and roller bearings.
Conventional circular bearings are disadvantaged in high performance applications due to tendencies to promote shaft instabilities at high speeds, low load conditions. More recently, non-circular types of bearings have been developed which provide good shaft stability. In particular, the wave bearing disclosed in U.S. Pat. No. 5,593,230, in which a waved profile is circumscribed on the inner bearing diameter with a wave amplitude equal to a fraction of the bearing clearance, has been designed and validated for use in general aviation gas turbines. However, theoretical studies have indicated concerns with wave bearings under blade out conditions and after oil interruption, where wave bearings are believed to have poor tolerance.
Wave bearings are disclosed and have been described, for example, in Dimofte, F. “Wave Journal Bearing with Compressible Lubricant—Part I: The Wave Bearing Concept and a Comparison to the Plain Circular Bearing,” STLE Tribology Transactions, Vol. 38(1), pp. 153-160 (1995). The use of wave bearings with oil lubricants at conventional temperatures is described in Dimofte, F.; Proctor, M. P.; Fleming, D. P.; Keith, T. G., Jr. “Wave Fluid Film Bearing Tests for an Aviation Gearbox,” Technical Memorandum, NASA TM-2000-209766, January, 2000. However, theoretical (analytical) studies investigating use of wave bearings under conditions of high temperature and high speed indicated problems are found in experimental studies at an oil temperature of 120° C.
Therefore, there remains a need for a method of lubricating bearings at higher temperatures and higher speeds, with reliable performance. The present invention meets this need.